SUBORDER D ARTIODACTYLA 207 



arise in the postero-frontal region, above or behind the more or less prominent 

 and entirely closed orbits. These appendages are either solid or more 

 frequently pneumatic in nature, and their hollow bases communicate with the 

 air-cavities in the frontal bones. They are placed between the orbits, and in 

 the more primitive forms are either erect or directed obliquely backward. 

 In the extreme forms (Bos) they become displaced backward and outward, 

 and appear on the posterior corners of the skull, being directed nearly at 

 right angles and horizontally outward. The nasal, maxillary and lachrymal 

 bones ai^e generally strongly developed, but the zygomatic arch is slender and 

 short. Lachrymal fossae and ethmoidal vacuities are frequently present in 

 the antelope, but are wanting in the ox, sheep and goat. 



The dentition is incomplete and much reduced, especially above, being 

 without incisor and canine teeth. As in all ruminants, the inferior canine 

 stands close to the incisors and functions as such. In the more primitive 

 forms (fossil antelopes) the selenodont cheek teeth remain brachyodont ; in 

 the more specialised forms they are hypsodont and at times distinctly 

 prismatic. As a rule the enamel is smooth, more rarely wrinkled. Basal 

 cingula occur only in the antelopes ; small accessory pillars are either absent 

 or may become unusually stout (Bovinae). In the superior molars the 

 ectoloph comprises two crescent-shaped plates strengthened by vertical folds ; 

 the crescentic internal cusps usually form closed pits. The premolars are 

 short, consisting of an ectoloph and one internal crescent. The inferior 

 molars are characterised by their narrowness. The external crescents 

 resemble the internal ones, and the internal cusps the external ones of the 

 superior molars ; on the external side an accessory pillar sometimes arises. 

 The three inferior premolars consist of a backwardly sloping crest with 

 expanded processes on the internal side. The incisors, as well as the canine 

 immediately following, have spatulate crowns and differ but little from each 

 other. 



The superior milk cheek teeth are somewhat more elongated and irregular 

 than the molars, but usually possess the complete structure of the latter, the 

 foremost only having the anterior half compressed and the posterior half 

 reduced. The last inferior milk cheek tooth is trilobed, while the two anterior 

 are like the teeth replacing them. 



The skeleton does not differ essentially from that of the Cervicornia. The 

 lateral toes, however, reach an extreme degree of reduction. The median 

 metapodials remain distinct only in the embryonic condition, early uniting to 

 form a cannon bone more or less deeply furrowed anteriorly. Separate 

 proximal vestiges of the two lateral metapodials sometimes continue 

 (antelopes), but generally these also disappear. Lateral digits are frequently 

 present. The carpus and tarsus are constituted as in the deer, likewise the 

 uterus and placenta. 



The hollow-horned ruminants form the latest and most abundant group 

 among the ungulates. Not until the Eecent period do they attain the maximum 

 point of their development, and by their tendency to modification in breeding 

 show that a certain plasticity and juvenility is inherent in them. It is in 

 the Old World that the Cavicornia have chiefly developed and increased. 

 Africa now appears to be their centre of distribution ; in truth, however, 

 southern Asia and possibly southern Europe may form the place of origin of 

 the majority of the genera. Yet a certain part of the Cavicornia are derived 



